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    Hi,

    I have been studying this diagram:



    There are some things that don't quite add up to me though. From the diagram you can see that the equation for the displacement x is:

    x = Xcos(theta)

    When the dot is to the far right theta is zero so x is equal to X and you get maximum displacement which I am fine with.

    However, when the ball is above the center the displacement is zero but theta as it is given in the diagram doesn't make this work. When the ball is directly overhead there is no triangle you can draw so theta is zero again but this can't be the case as we know the displacement is zero at that point?
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    (Original post by Bibloski)
    Hi,

    I have been studying this diagram:



    There are some things that don't quite add up to me though. From the diagram you can see that the equation for the displacement x is:

    x = Xcos(theta)

    When the dot is to the far right theta is zero so x is equal to X and you get maximum displacement which I am fine with.

    However, when the ball is above the center the displacement is zero but theta as it is given in the diagram doesn't make this work. When the ball is directly overhead there is no triangle you can draw so theta is zero again but this can't be the case as we know the displacement is zero at that point?
    When the point is directly overhead,  \theta is not 0. It is  \frac{\pi}{2} since this is the angle made by the line connecting P and the centre of the circle with the horizontal diameter.
 
 
 
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